Effect of Airtight Building Enclosures in High-Rise Residential Buildings

David C. Young, P.E. Principal, Building Science Specialist

April 3, 2012

BEST3 – Atlanta, GA

Overview

Ventilation Background

Airflow in Tall Buildings

How Air-Leaky are High-Rise Multi-Unit Residential Buildings?

Effects of Poor Ventilation

Case Studies

Contributing Research at RDH for these studies: Shawn McIsaac, BASc. Graham Finch, M.Eng. Warren Knowles, P.Eng. Brian Hubbs, P.Eng.

Acknowledgements

Energy costs and Building Codes are driving tighter building enclosures Reduction of make-up air through enclosure Older HVAC systems relied on enclosure air leakage for make-up air – not designed to accommodate airtight enclosures (retrofits) Some new construction HVAC systems still rely on corridor pressurization for make-up air, but assumptions of enclosure air leakage rates have not kept pace with actual airtightness Leads to potential ventilation problems – condensation, mold, odors, poor indoor air quality (IAQ), etc.

Ventilation Background

Air Flows & Air Leakage in Multi-Unit Residential Buildings

Building pressures vary over the course of the day - year Can measure shell airtightness, but ignores windows, HVAC ducts and occupant behavior Interior airflows & difficult to predict We have a good qualitative sense of airflow and leakage but not necessarily quantitative back-up

Ventilation Air Flow within Multi-Unit Residential Buildings

Ventilation Strategies & Air Leakage are inter-related

2012 International Energy Conservation Code (IECC) introduces air barrier and air leakage requirements nationally

Air Barrier Compliance Options C402.4.1.2 • Materials 0.004 cfm/ft2 @ 75Pa (C402.4.1.2.1)

ASTM E 2178 “Standard Test Method for Air Permeance of Building Materials”

• Assemblies 0.04 cfm/ft2 @ 75Pa (C402.4.1.2.2) ASTM E 2357 “Standard Test Method for Determining Air Leakage of Air Barrier Assemblies”

• Whole Building 0.4 cfm/ft2 @ 75Pa (C402.4.1.2.3) ASTM E779 Standard Test Method for Determining Air Leakage Rate by Fan Pressurization

Washington State Energy Code requires Whole Building air leakage testing for buildings over 5-stories, but building does not have to pass prescribed value (yet)

How Air-Leaky Can Building Enclosures Be?

Standard Equivalent Normalized Leakage Rate

ASHRAE – “Tight” enclosure 0.10 cfm/ft2 @ 75 Pa (0.027 cfm/ft2 @ 10 Pa)

R2000 Standard – enclosure 0.13 cfm/ft2 @ 75 Pa (0.035 cfm/ft2 @ 10 Pa)

US Army Corps – enclosure 0.25 cfm/ft2 @ 75 Pa (0.067 cfm/ft2 @ 10 Pa)

ASHRAE – “Average” enclosure 0.30 cfm/ft2 @ 75 Pa (0.081 cfm/ft2 @ 10 Pa)

ASTM E779 – Whole Building 0.40 cfm/ft2 @ 75 Pa (0.11 cfm/ft2 @ 10 Pa)

2012 International Energy Conservation Code (IECC) - Enclosure Leakage

0.40 cfm/ft2 @ 75 Pa (0.11 cfm/ft2 @ 10 Pa)

ASHRAE – “Leaky” enclosure 0.60 cfm/ft2 @ 75 Pa (0.16 cfm/ft2 @ 10 Pa)

Various Whole Building Airtightness Standard Targets

LEAK

IER

TIGH

TER

@10 Pa calculated assuming n=0.65

Typical Energy Consumption: 1980s-1990s MURB Average of 11 typical study buildings - Total 206 kWh/ m2/ yr

Units of kwh/ m2/ yr, % total Energy Study – Vancouver and Victoria, B.C.

Typical Energy Consumption: Post 2000/ Modern MURB Average of several typical modern MURBs– Total >222 kWh/ m2/ yr

Units of kwh/ m2/ yr, % total Typically up from <50 to up to 150 cfm/unit Energy Study – Vancouver and Victoria, B.C.

Inefficiencies of pressurized corridor ventilation and poor thermally performing building enclosure masks true absolute importance of enclosure air leakage in MURBs For energy efficient buildings we need to de-couple ventilation from heating – move away from pressurized corridor approach to in-suite HRVs or central heat-recovery ducted to units (and health/ IAQ) Interior airtightness is critical to enclosure airtightness in terms of energy efficiency for MURBs – as it allows for compartmentalization – which allows for much more efficient ventilation strategies to be used

Interior Airtightness & Ventilation

Impact of Heat Recovery Ventilation & Efficient Enclosure

Electric Baseboard Heating, 3.3, 3%

Ventilation Heating, 6.4, 6%

DHW, 32.9, 29%

Lights - Common, 3.7, 3%

Lights - Suite, 15.9, 14%

Plug and Appliances (Suites), 18.8, 16%

Equipment and Ammenity (Common),

28.3, 25%

Elevators, 4.2, 4%

More Efficient MURB ~114 kWh/ m2 Energy Study – Vancouver and Victoria, B.C.

For in-suite ducted (rooftop or direct wall) ventilation work in high-rises, building pressures must be addressed:

Significantly reduce Stack Effect by compartmentalizing units and corridors from shafts /elevators/stairwells Construct airtight floors & walls Balance mechanical pressures In-suite ventilation systems require special maintenance – design consideration

Significant Energy Savings Potential for MURBs Expensive to add in-suite ventilation to existing buildings

In-Suite Ventilation Systems

Effects of Poor Ventilation Contamination Build-up Condensation Fungal Growth Health Problems

What symptoms are often linked to poor indoor air quality? It is common for people to report one or more of the following

symptoms: dryness and irritation of the eyes, nose, throat, and skin headache fatigue shortness of breath hypersensitivity and allergies sinus congestion coughing and sneezing dizziness nausea

Effects of Poor Ventilation

How does mechanical ventilation alleviate problems with condensation and contaminants?

Regular and predictable removal of moisture and contaminants through bathroom fans Dilution of contaminants and moisture with fresh heated outdoor air

Effects of Poor Ventilation

Case Studies

Central Park Place, Burnaby, B.C. – Existing Building The Strand, Portland, OR – New Construction

Three 22-story condominium towers – 1960s Window replacement and building enclosure rehabilitation – 2011 Significantly increased airtightness of enclosure Resulted in some poor Indoor Air Quality issues HVAC system relies on corridor pressurization and opening windows Improvements to Existing System Proposed

Central Park Place – Burnaby, BC

Condensation Related to lack of ventilation Build-up of moisture Typically collects on the coldest surfaces

Existing Conditions

Fungal Growth Related to condensation Moisture can support fungal growth

Other IAQ issues

Existing Conditions

Observations of Existing System

Building Enclosure Pre-rehab Air leakage through walls and interfaces Some leakage through ducts Natural uncontrolled air exchange through windows and doors Uncontrolled leakage through adjacent walls

Building Enclosure Post-rehab Air leakage to the outside is close to zero through the upgraded walls, windows and doors Most of the air leakage in each unit is through the fan ducts Opening a window can increase natural ventilation if there is a pressure differential Still have uncontrolled leakage through adj. walls

Observations of Existing System

Bathroom Fans Installed in every unit Some ability to exhaust unit

24 units were visited > 8 in East tower > 7 in North tower > 9 in West tower

Flow rates varied from 12 cfm to 42 cfm (recommended 50-60cfm) Fans are loud making operation intrusive Fans were not operational in 2 units

Observations of Existing System

Approximate Fresh Air Supplied ( East Tower)

2nd floor – 110 cfm 4th floor – 0 cfm 7th floor – 250 cfm 12th floor – 90 cfm 16th floor – 250 cfm

ASHRAE 62.1 Design Supply = ~400 cfm per floor

Design - ~9000 cfm whole building Current - 3000-6000 cfm whole building

Observations of Existing System

1/ 3 to 2/ 3 of ASHRAE

requirement

Pressure Differential Across Unit Doors Review of 36 units on 5 different floors • Floors 2, 4 and 7 – 16 units (44%) had airflow out to corridor • Floors 12, 16 – 7 units (19%) had inward air flow beneath door;

but much less than ASHRAE 62.1 standards • Total of 13 units ( 36%) had no door undercut

Observations of Existing System

Note on Original Mechanical Drawings: “Each floor area is vented by means of openable windows or sliding doors”

Existing System Design

Recommendations – Central Park Place

Incremental Approach

Operation of Windows and Doors Adjust Door Undercuts Replace Bathroom Fans New Make-Up Air Unit (MAU)

Increase Natural Ventilation with Windows and Doors Limited effectiveness thus far Not practical in winter Heating outdoor air, warm air escaping Energy efficiency

Recommendations

Adjust Door Undercuts Ensures air enters the units

Recommendations

Make-Up Air Unit New energy efficient unit New exhaust grilles on each floor Delivers fresh, pre-heated air to each floor Adequately pressurize hallways to ensure fresh air to units Currently only supplying 3000cfm - 6000 cfm • ASHRAE 62.1 design 9000 cfm

Recommendations

New Bathroom Fans Exhaust contaminants from units Quieter than existing fans Timer controlled operation as well as occupant controlled Larger design capacity

Recommendations

$0$200$400$600$800

$1,000$1,200$1,400$1,600$1,800$2,000

In-SuiteHRV New Fans +

MAU New Fansonly

Project CostsHRVMAUFan Cost

Mechanical Upgrade Costs per Unit – Summary

Case Study – The Strand – Portland, OR

12-story condominium building completed in 2006 Some units experienced condensation issues shortly after occupancy Condensation occurred on thermally broken aluminum window-wall system RDH performed monitoring study of interior conditions in 6 units (2 control units) Make-up air relies on corridor pressurization

33 of Total

Window Problem??

Typical Unit Layout

34 of Total

Logger Installation

Data logging equipment installed in various locations Also connected to fan AC current to monitor usage

Average Window Temperatures During a Condensation Occurrence

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Average Window Temperatures During Condensation

The average window temperatures in the condensation unit are equal to or higher than the corresponding control unit This indicates window construction is not the causal factor

Control Suite Condensation Suite

Effect of HVAC Use on Window Temperatures

Control Unit

Condensation Unit

Effect of HVAC Use on Window Temperatures

Thermostat set at 70° F results in steady window temperatures of +/ - 65° F

Window temperature steadily declines when the furnace is turned off (night) Window temperatures drop between 58-61° F

Condensation occurs

Control Unit Condensation Unit

Effect of Fan Use/ Increased Makeup Air on Unit Dew Point

Effect of Fan Use/ Increased Makeup Air on Suite Dew Point

Shower occurs without bathroom fan, kitchen fan is run for 3 hrs, overall dew point throughout the unit decreases

Shower #2 occurs again no bath-room fan AND no kitchen fan, overall unit dew point does not equalize for 10-12hrs.

The bathroom dew point does not recover

CO2 Levels Indicate Volume of Fresh Air Exchange

CO2 Levels Indicate Volume of Fresh Air Exchange

Control units W602 and E902 both have low average CO2 levels indicating higher air exchange rates No coinciding condensation in either unit

Unit W302 has an average CO2 50% higher than the other units indicating a significantly lower air exchange rate There is coinciding condensation in unit

Most Significant Factors in Condensation

Lack of ventilation make up air under door (+ high RH) Poor air distribution to windows from heating vents Lack of HVAC and exhaust fan use by occupants

Recommendations – The Strand

Increase Ventilation Air Increase Exhaust Air Address Occupant Load

45 of Total

Direct all heating supply vent grills at the window sills. Particular attention should be focused on exterior corners where temperatures are lowest Program in-suite HVAC unit to continuously circulate air for at least 30 minutes after each heating cycle Balance corridor pressurization to remain positive to unit

Recommendations – Increase Ventilation Air

Install continuous exhaust fan in master bathroom, or run dryer booster fan to continuously exhaust air from the unit Equip bathroom fans with humidistat-controlled switch, or occupant sensor and timer to ensure the fans are exhausting during entire elevated moisture periods (Humidistat or timer should not be user adjustable)

Recommendations – Increase Exhaust Air

Maintain an interior temperature at 70°F during cold winter months

Minimize or open window coverings during periods of cold exterior temperatures

Crack open windows during cold weather (about ¼ ”)

Open interior doors to allow air circulation

Run kitchen fans when cooking

Run bathroom fans when showering and bathing until moisture build-up is fully evacuated

Ensure clean dryer vents and lint traps

Recommendations – Address Occupant Load

Summary of Findings

Existing Buildings Be aware of effects of tightening enclosure during retrofits Consider adding continuous operation exhaust fans Balance corridor ventilation (add MAU if necessary) Check and improve undercut at entry doors Add in-suite ventilation (HRVs) where feasible Provide operating information to occupants

New Construction Compartmentalize units De-couple ventilation from heating/cooling (HRVs) Locate heating source near windows to “wash” with warm air Provide continuous exhaust Provide operating information to occupants

Summary of Findings

Questions